Android: how to build original boot.img and system.img.ext4

#boot.img

\>mkbootimg --kernel --ramdisk --cmdline --output

e.g.

\>mkbootimg --kernel ./kernel --ramdisk ./ramdisk.img --cmdline "console=ttyHSL0,115200,n8 androidboot.hardware=qcom" --base 0x40200000 --pagesize 2048 --output boot.img

#system.img.ext4

\>mkuserimg.sh ./system.img.ext4 ext4 system 115343360

\>make_ext4fs -l 115343360 -a system ./system.img.ext4 ./target/product/XXX/system

How to repack these images

http://android-dls.com/wiki/index.php?title=HOWTO:_Unpack,_Edit,_and_Re-Pack_Boot_Images